Coaxial cable including tubular bimetallic inner layer with folded edge portions and associated methods

ABSTRACT

A coaxial cable may include an inner conductor, an outer conductor, and a dielectric material therebetween. The inner conductor may include a tubular bimetallic layer having a pair of opposing longitudinal edge portions at a longitudinal seam. The tubular bimetallic layer may include an inner metal layer and an outer metal layer bonded thereto. At least one of the opposing longitudinal edge portions may define at least one folded edge portion including an end portion of the inner metal layer extending beyond a corresponding end portion of the outer metal layer and being folded adjacent thereto and defining a non-joined interface therewith. The longitudinal seam may include a welded joint between at least portions of the inner metal layer.

FIELD OF THE INVENTION

The present invention relates to the field of communications, and, moreparticularly, to coaxial cables and associated methods for making thecoaxial cables.

BACKGROUND OF THE INVENTION

Coaxial cables are widely used to carry high frequency electricalsignals. Coaxial cables enjoy a relatively high bandwidth, low signallosses, are mechanically robust, and are relatively low cost. A coaxialcable typically includes an elongate inner conductor, a tubular outerconductor, and dielectric separating the inner and outer conductors. Forexample, the dielectric may be a plastic foam material. An outerinsulating jacket may also be applied to surround the outer conductor.

One particularly advantageous use of coaxial cable is for connectingelectronics at a cellular or wireless base station to an antenna mountedat the top of a nearby antenna tower. For example, the transmitter andreceiver located in an equipment shelter may be coupled via coaxialcables to antennas carried by the antenna tower. A typical installationincludes a relatively large diameter main coaxial cable extendingbetween the equipment shelter and the top of the antenna tower tothereby reduce signal losses. For example, CommScope, Inc. of Hickory,N.C. offers its CellReach® coaxial cable for such applications.

In larger diameter coaxial cables, which are commonly used in cellularcommunication as described above, the elongate inner conductor can betubular in shape. The tubular inner conductor may also surround an innerdielectric material. The inner conductor is typically manufactured byforming a flat layer or sheet of conductive material into a tube with alongitudinal seam and welding the seam to form a continuous joint. Theouter conductor is also similarly manufactured by forming a flat layeror metal sheet into a tube with a longitudinal seam that is welded toform a continuous joint.

The high frequency signals carried by the coaxial cable are concentratedin only a small portion, radially outermost, of the inner conductor, anda correspondingly small radially innermost portion of the outerconductor. This characteristic is attributed to the electromagneticphenomenon called the skin effect. Therefore, only the thin outer radialportion of the tubular inner conductor carries the high frequencytransmission. Conversely, the outer tubular conductor also carries thehigh frequency signals in the thin radially innermost portion.

Bimetallic layers have been used for the inner and/or outer tubularconductors in a coaxial cable where a higher conductivity and moreexpensive metal is used to provide the radially outermost portion of aninner conductor, and is used to provide the radially innermost portionof the outer conductor. For example, the outermost layer of the innerconductor may include a relatively costly and highly conductive metalsuch as copper, and the inner layer of the inner conductor may include aless costly and less conductive metal, such as aluminum. For example,U.S. Pat. No. 6,717,493 B2 to Chopra et al. and U.S. Patent ApplicationNo. 2004/0118591 A1 to Bufanda et al. each discloses a coaxial cablewith such bimetallic tubular inner conductors.

Notwithstanding the benefits of a bimetal tubular inner conductor, theremay be some shortcomings. For example, the manufacture of a bimetaltubular inner conductor usually involves some form of heat basedwelding, such as for example, conventional induction welding, to weldthe seam to form a welded joint. Unfortunately, the two metals that formthe bimetal tubular inner conductor usually have different meltingtemperatures. For example, copper and aluminum are commonly used as theouter and inner layers of the inner conductor, respectively. Copper hasa melting point of 1100° C. and a conductivity of 59.6×10⁶ S·m⁻¹, whilealuminum has a lower melting point of 660° C. and a lower conductivityof 37.8×10⁶ S·m⁻¹. This disparity in melting points makes welding of thejoint relatively difficult.

In response to this particular shortcoming in manufacture of bimetaltubular inner conductors, coaxial cable manufacturers have developed acoaxial cable with a bimetal tubular inner conductor comprising aninlaid bimetallic layer, such as disclosed, for example, in U.S. Pat.No. 6,342,677 to Lee. This coaxial cable is more easily welded sinceonly the inner metal layer is welded during manufacture of the bimetaltubular inner conductor. Nonetheless, the inlaid bimetal inner conductoris relatively costly to manufacture. Of course, similar considerationsapply to the outer conductor of a coaxial cable. That is a conventionalbimetallic layer may be difficult to weld, and an inlaid bimetalliclayer may be relatively expensive.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to provide a coaxial cable including an innerconductor fabricated using a less expensive tubular bimetallic layerthat is also readily welded at its longitudinal seam.

This and other objects, features, and advantages in accordance with thepresent invention are provided by a coaxial cable that may comprise aninner conductor comprising a tubular bimetallic layer having a pair ofopposing longitudinal edge portions at a longitudinal seam. The tubularbimetallic layer may include an inner metal layer and an outer metallayer bonded thereto. At least one of the opposing longitudinal edgeportions may define at least one folded edge portion comprising an endportion of the inner metal layer extending beyond a corresponding endportion of the outer metal layer and being folded adjacent thereto anddefining a non-joined interface therewith. In some embodiments, thefolded end portion may be folded at a right angle adjacent thecorresponding end portion of the outer metal layer. In otherembodiments, the folded end portion may comprise an end portion of theinner metal layer extending beyond a corresponding end portion of theouter metal layer and being folded over onto itself adjacent thecorresponding end portion of the outer metal layer and defining anon-joined interface therewith. In addition, the longitudinal seam maycomprise a welded joint between at least portions of the inner metallayer. Accordingly, a less expensive starting material may be used forthe inner conductor, that is, a simple bimetallic strip, as compared tothe more expensive inlaid bimetallic strip, for example.

The at least one folded edge portion may comprise both of the opposinglongitudinal edge portions, for example. The inner metal layer may havea lower melting temperature than the outer metal layer. The outer metallayer may also have a higher electrical conductivity than the innermetal layer. For example, the inner metal layer may comprise aluminum,and the outer metal layer may comprise copper.

The tubular bimetallic layer may have a thickness in a range of about0.005 to 0.050 inches. The outer metal layer may have a percentagethickness relative to an overall thickness of the tubular bimetalliclayer in a range of about 1 to 30%. The coaxial cable may also compriseanother dielectric material layer filling the inner conductor. Inaddition, the cable may further comprise an insulating jacketsurrounding the outer conductor.

A method aspect is for making a coaxial cable comprising an innerconductor, an outer conductor and a dielectric material layer betweenthe inner and outer conductors. More particularly, forming the innerconductor may include forming a bimetallic strip into a tubularbimetallic layer having a pair of longitudinal edge portions andcomprising an inner metal layer and an outer metal layer bonded thereto,with at least one of the longitudinal edge portions defining a foldededge portion comprising an end portion of the inner metal layerextending beyond a corresponding end portion of the outer metal layerbeing folded adjacent thereto and defining a non-joined interfacetherewith. The method may further include welding at least portions ofthe longitudinal seam to form a welded joint between at least portionsof the inner metal layer. The method may also include forming thedielectric material layer surrounding the inner conductor, and formingthe outer conductor surrounding the dielectric material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective end view of a coaxial cable in accordance withthe present invention.

FIG. 2 is an enlarged cross-sectional view of a portion of the tubularbimetallic inner conductor of the coaxial cable of FIG. 1 shown prior towelding.

FIG. 3 is an enlarged cross-sectional view of the portion of the tubularbimetallic inner conductor of the coaxial cable of FIG. 1 shown afterwelding.

FIG. 4 is an enlarged cross-sectional view of a portion of a tubularbimetallic inner conductor of a coaxial cable of another embodimentshown prior to welding.

FIG. 5 is an enlarged cross-sectional view of the portion of the tubularbimetallic inner conductor of FIG. 4 shown after welding.

FIG. 6 is an enlarged cross-sectional view of a portion of a tubularbimetallic inner conductor of a coaxial cable of another embodimentshown prior to welding.

FIG. 7 is an enlarged cross-sectional view of the portion of the tubularbimetallic inner conductor of FIG. 6 shown after welding.

FIG. 8 is an enlarged cross-sectional view of a portion of a tubularbimetallic inner conductor of a coaxial cable of yet another embodimentshown prior to welding.

FIG. 9 is an enlarged cross-sectional view of the portion of the tubularbimetallic inner conductor of FIG. 8 shown after welding.

FIG. 10 is schematic diagram of an apparatus for making a coaxial cablein accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime notation is used toindicate similar elements in alternative embodiments.

Referring initially to FIGS. 1-3, a coaxial cable 21 in accordance withthe present invention is described. The coaxial cable 21 illustrativelyincludes an inner conductor 23, an outer conductor 25, and a dielectricmaterial layer 24 between the inner and outer conductors. The innerconductor 23 illustratively includes a tubular bimetallic layer 33having a pair of opposing longitudinal edge portions at a longitudinalseam 27. The tubular bimetallic layer 33 illustratively includes aninner metal layer 32 and an outer metal layer 31 bonded thereto.

The tubular bimetallic layer 33 illustratively includes one of theopposing longitudinal edge portions comprising an end portion 61 of theinner metal layer 32 extending outwardly beyond the outer metal layer 31and being folded over onto itself adjacent the outer metal layer anddefining a non-joined interface 34 therewith.

The outer metal layer 31 may have a higher electrical conductivity thanthe inner metal layer 32 to facilitate signal carrying ability at theskin depth, for example. The inner metal layer 32 may have a lowermelting temperature and a lower cost than the outer metal layer 31. Thelower melting temperature of the inner metal layer 32 facilitateswelding, for example. The inner metal layer 32 may comprise aluminum orany suitable metal as appreciated by a person skilled in the art, andthe outer metal layer 31 may comprise copper or any suitable metal asappreciated by those skilled in the art.

The tubular bimetallic layer 33 may have a thickness in a range of about0.005 to 0.050 inches, and the outer metal layer 31 may have apercentage thickness relative to an overall thickness of the tubularbimetallic layer 33 in a range of about 1 to 30.

As shown perhaps best in FIG. 3, the longitudinal seam 27 illustrativelyincludes a welded joint 63 between at least portions of the inner metallayer 32. The coaxial cable 21 illustratively comprises anotherdielectric material layer 22 filling the tubular bimetallic layer 33 andan insulating jacket 26 surrounding the outer conductor 25. Of course,welding may cause at least some portion of the non-joined interface 34to become joined as will be appreciated by those skilled in the art.

Referring now additionally to FIGS. 4-5, another embodiment is nowdescribed. In this embodiment of the coaxial cable 21′, those elementsalready discussed above with respect to FIGS. 1-3 are given primenotation and most require no further discussion herein. This embodimentdiffers from the previous embodiment in that both of the opposinglongitudinal edge portions illustratively include end portions 61′, 62′of the inner metal layer 32′ extending outwardly beyond the outer metallayer 31′ and being folded over onto themselves adjacent the outer metallayer and defining non-joined interfaces 34′, 54′ therewith. Of course,welding may cause at least some portions of the non-joined interfaces34′, 54′ to become joined as will be appreciated by those skilled in theart.

Referring now additionally to FIGS. 6-7, another embodiment is nowdescribed. In this embodiment of the coaxial cable 21″, those elementsalready discussed above with respect to FIGS. 1-3 are given double primenotation and most require no further discussion herein. This embodimentdiffers from the previous embodiment in that the opposing longitudinaledge portions illustratively include one end portion 61″ of the innermetal layer 32″ extending outwardly beyond the outer metal layer 31″ andbeing folded at a right angle adjacent the outer metal layer anddefining a non-joined interface 34″ therewith. After welding, as shownperhaps best in FIG. 7, a welded joint 63″ is formed between theadjacent portions of the inner metal layer

Referring now additionally to FIGS. 8-9, another embodiment is nowdescribed. In this embodiment of the coaxial cable 21′″, those elementsalready discussed above with respect to FIGS. 6-7 are given triple primenotation and most require no further discussion herein. This embodimentdiffers from the previous embodiment in that each of the opposinglongitudinal edge portions illustratively includes an end portion 61′″,62′″ of the inner metal layer 32′″ extending outwardly beyond the outermetal layer 31′″ and being folded at a right angle adjacent the outermetal layer and defining a non-joined interface 34′″, 54′″ therewith.

Referring additionally to FIG. 10, another aspect relates to a methodand associated apparatus 200 for making a coaxial cable 21 that maycomprise the inner conductor 23 including tubular bimetallic layer 33,outer conductor 25, and dielectric material layer 24 therebetween. Adielectric material rod 212 and a supply reel 201 of the bimetallicstrip with a pair of longitudinal edge portions are provided. Thebimetallic strip may comprise an inner metal layer and an outer metallayer bonded thereto. The supply reel 201 of bimetallic strip may beprovided with at least one of the longitudinal edge portions with an endportion of the inner metal layer extending outwardly beyond the outermetal layer. Further, the supply reel 201 of bimetallic strip may alsobe provided comprising the end portion folded over onto itself adjacentthe outer metal layer and defining a non-joined interface therewith.

In the alternative, the supply reel 201 of bimetallic strip may be fedinto a trimmer/folder 202, shown with dashed lines, which illustrativelytrims at least one of the longitudinal edge portions to provide an endportion of the inner metal layer extending outwardly beyond the outermetal layer. The trimmer/folder 202 may trim the metal layer using adiamond or other blade, or any other trimming techniques as will beappreciated by those skilled in the art. Further, the trimmer/folder 202illustratively folds the end portion over onto itself adjacent the outermetal layer and defining a non-joined interface therewith.

Further and as discussed above, the outer metal layer may have a higherelectrical conductivity than the inner metal layer. The inner metallayer may have a lower melting temperature than the outer metal layer.The inner metal layer may comprise aluminum or any suitable metal asappreciated by a person skilled in the art, and the outer metal layermay comprise copper or any suitable metal as appreciated by a personskilled in the art. The tubular bimetallic layer may have a thickness ina range of about 0.005 to 0.050 inches, and the outer metal layer mayhave a percentage thickness relative to an overall thickness of thetubular bimetallic layer in a range of about 1 to 30%.

The dielectric material rod 212 and the supply reel 201 of bimetallicstrip are fed into the tube former 203, which illustratively forms thebimetallic strip into a tubular bimetallic layer having a pair ofopposing longitudinal edge portions at a longitudinal seam to providethe inner conductor comprising tubular bimetallic layer.

As will be appreciated by those skilled in the art, the dielectricmaterial may be disposed inside the inner tube downstream from the tubeformer 203, or thereafter using settable material as described in U.S.Pat. No. 6,915,564. The output of the tube former 203 is then fed intothe induction welder 204, which illustratively welds the longitudinalseam to form a welded joint between at least portions of the inner metallayer. The output of the induction welder 204 is then fed into thedielectric extruder 205, which illustratively forms the dielectricmaterial layer surrounding the inner conductor.

The output of the dielectric extruder 205 is then fed along with asupply reel 207 of metallic strip into a second tube former 206, whichillustratively forms the outer conductor surrounding the dielectricmaterial layer.

The output of the second tube former 206 is fed into a second inductionwelder 209, which illustratively welds the outer conductor. The outputof the second induction welder 209 is fed into the jacket extruder 210,which forms an insulating jacket surrounding the outer conductor. Thecompleted coaxial cable 21 is output from the jacket extruder 210 fortake-up by a suitable take-up reel, not shown.

In other embodiments, the supply reel 201 of bimetallic strip may beprovided with at least one of the longitudinal edge portions with an endportion of the inner metal layer extending outwardly beyond the outermetal layer. Further, the supply reel 201 of bimetallic strip may beprovided comprising the end portion folded at a right angle adjacent theouter metal layer and defining a non-joined interface therewith.

This application is related to copending patent applications entitled,COAXIAL CABLE INCLUDING TUBULAR BIMETALLIC INNER LAYER WITH BEVELLEDEDGE JOINT AND ASSOCIATED METHODS, attorney work docket number 63235;COAXIAL CABLE INCLUDING TUBULAR BIMETALLIC INNER LAYER WITH ANGLED EDGESAND ASSOCIATED METHODS, attorney work docket number 63236; COAXIAL CABLEINCLUDING TUBULAR BIMETALLIC OUTER LAYER WITH BEVELLED EDGE JOINT ANDASSOCIATED METHODS, attorney work docket number 63248; COAXIAL CABLEINCLUDING TUBULAR BIMETALLIC OUTER LAYER WITH ANGLED EDGES ANDASSOCIATED METHODS, attorney work docket number 63249; and COAXIAL CABLEINCLUDING TUBULAR BIMETALLIC OUTER LAYER WITH FOLDED EDGE PORTIONS ANDASSOCIATED METHODS, attorney work docket number 63250 which are filed onthe same date and by the same assignee and inventors, the disclosures ofwhich are hereby incorporated by reference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A coaxial cable comprising: an inner conductor, an outer conductorand a dielectric material layer therebetween; said inner conductorcomprising a tubular bimetallic layer having a pair of opposinglongitudinal edge portions at a longitudinal seam; said tubularbimetallic layer comprising an inner metal layer and an outer metallayer bonded thereto; at least one of the opposing longitudinal edgeportions defining at least one folded edge portion comprising an endportion of said inner metal layer extending beyond said outer metallayer and being folded adjacent thereto and defining a non-joinedinterface therewith; the longitudinal seam comprising a welded jointbetween at least portions of said inner metal layer.
 2. A coaxial cableaccording to claim 1 wherein the at least one folded edge portion isfolded at a right angle adjacent the corresponding end of said outermetal layer.
 3. A coaxial cable according to claim 1 wherein the atleast one folded edge portion is folded over onto itself adjacent thecorresponding end of said outer metal layer.
 4. A coaxial cableaccording to claim 1 wherein the at least one folded edge portioncomprises both of the opposing longitudinal edge portions.
 5. A coaxialcable according to claim 1 wherein said outer metal layer has a higherelectrical conductivity than said inner metal layer.
 6. A coaxial cableaccording to claim 1 wherein said inner metal layer has a lower meltingtemperature than said outer metal layer.
 7. A coaxial cable according toclaim 1 wherein said inner metal layer comprises aluminum; and whereinsaid outer metal layer comprises copper.
 8. A coaxial cable according toclaim 1 wherein said tubular bimetallic layer has a thickness in a rangeof about 0.005 to 0.050 inches.
 9. A coaxial cable according to claim 1wherein said outer metal layer has a percentage thickness relative to anoverall thickness of said tubular bimetallic layer in a range of about 1to 30%.
 10. A coaxial cable according to claim 1 further comprisinganother dielectric material layer filling said tubular bimetallic layer.11. A coaxial cable according to claim 1 further comprising aninsulating jacket surrounding said outer conductor.
 12. A coaxial cablecomprising: an inner conductor, an outer conductor and a dielectricmaterial layer therebetween; said inner conductor comprising a tubularbimetallic layer having a pair of opposing longitudinal edge portions ata longitudinal seam; said tubular bimetallic layer comprising an innermetal layer and an outer metal layer bonded thereto, said outer metallayer having a higher electrical conductivity than said inner metallayer, and said inner metal layer having a lower melting temperaturethan said outer metal layer; at least one of the opposing longitudinaledge portions comprising an end portion of said inner metal layerextending beyond a corresponding end portion of said outer metal layerand being folded over onto itself adjacent the corresponding end of saidouter metal layer and defining a non-joined interface therewith; thelongitudinal seam comprising a welded joint between at least portions ofsaid inner metal layer.
 13. A coaxial cable according to claim 12wherein the at least one folded edge portion comprises both of theopposing longitudinal edge portions.
 14. A coaxial cable according toclaim 12 wherein said inner metal layer comprises aluminum.
 15. Acoaxial cable according to claim 12 wherein said outer metal layercomprises copper.
 16. A coaxial cable according to claim 12 wherein saidtubular bimetallic layer has a thickness in a range of about 0.005 to0.050 inches.
 17. A coaxial cable according to claim 12 wherein saidouter metal layer has a percentage thickness relative to an overallthickness of said tubular bimetallic layer in a range of about 1 to 30%.18. A coaxial cable according to claim 12 further comprising anotherdielectric material layer filling said tubular bimetallic layer; and aninsulating jacket surrounding said outer conductor.
 19. A method formaking a coaxial cable comprising an inner conductor, an outer conductorand a dielectric material layer therebetween, the method comprising:forming the inner conductor by at least forming a bimetallic strip intoa tubular bimetallic layer having a pair of longitudinal edge portionsand comprising an inner metal layer and an outer metal layer bondedthereto, at least one of the longitudinal edge portions defining atleast one folded edge portion comprising an end portion of the innermetal layer extending beyond a corresponding end portion of the outermetal layer and being folded adjacent thereto and defining a non-joinedinterface therewith, and welding at least portions of the longitudinalseam to form a welded joint between at least portions of the outer metallayer; forming the dielectric material layer surrounding the innerconductor; and forming the outer conductor surrounding the dielectricmaterial layer.
 20. A method according to claim 19 wherein the outermetal layer has a greater electrical conductivity than the inner metallayer, and the inner metal layer has a lower melting temperature thanthe outer metal layer.
 21. A method according to claim 22 wherein theinner metal layer comprises aluminum; and wherein the outer metal layercomprises copper.
 22. A method for making a coaxial cable comprising aninner conductor, an outer conductor and a dielectric material layertherebetween, the method comprising: forming the inner conductor by atleast forming a bimetallic strip into a tubular bimetallic layer havinga pair of longitudinal edge portions and comprising an inner metal layerand an outer metal layer bonded thereto, at least one of thelongitudinal edge portions defining at least one folded edge portioncomprising an end portion of the inner metal layer extending beyond acorresponding end portion of the outer metal layer and being folded overonto itself adjacent the corresponding end portion of the outer metallayer and defining a non-joined interface therewith, and welding atleast portions of the longitudinal seam to form a welded joint betweenat least portions of the outer metal layer; forming the dielectricmaterial layer surrounding the inner conductor; and forming the outerconductor surrounding the dielectric material layer.
 23. A methodaccording to claim 22 wherein the outer metal layer has a greaterelectrical conductivity than the inner metal layer, and the inner metallayer has a lower melting temperature than the outer metal layer.
 24. Amethod according to claim 22 wherein the inner metal layer comprisesaluminum; and wherein the outer metal layer comprises copper.